The present invention relates to a two-way variable-section control valve, particularly for controlling the evaporation pressure of a refrigeration circuit, and which may be used to advantage, though not exclusively, in aircraft air conditioning systems.
Known valves of the above type substantially comprise a body having an inlet conduit and an outlet conduit for refrigerant; and a movable member for choking the section of a refrigerant passage between the inlet and the outlet.
The movable member is normally controlled by a thermal actuator comprising a heat-sensitive element, and an output member which is moved by and according to the temperature of the heat-sensitive element, the temperature of which may be varied by means of an electric resistor and controlled electronically. The heat-sensitive element normally comprises one or more bimetallic blades deformable alongside a variation in temperature, or a deformable bulb containing a liquid in equilibrium with its saturated vapor.
Known valves of the type briefly described above present several drawbacks.
In particular, response is normally poor, due to the time taken for the heat-sensitive element to cool when the heat supplied by the resistor is cut off.
Known valves are therefore only suitable for use in substantially static conditions, such as refrigerators or static room conditioners for maintaining a substantially constant temperature and involving only a gradual variation in load, and are totally unsuitable for use in widely and rapidly varying conditions such as those encountered, for example, in the cockpit of an aircraft.
Moreover, known valves are normally sensitive to ambient and/or refrigerant pressure, so that the operating point of the valve does not depend solely on the supply voltage of the electric resistor.
This further rules out the use of known valves on aircraft, which are obviously subject to widely varying altitudes and, hence, pressures.